Compressor having a control and diagnostic module

ABSTRACT

An apparatus includes a voltage sensor, a current sensor, and a controller. The voltage sensor measures voltage values of alternating current power supplied to a capacitor. The capacitor is electrically coupled to a compressor. The current sensor measures current values of the alternating current power. The controller is configured to receive the voltage values and the current values. The controller is configured to determine a first power factor value based on at least one of the voltage values and at least one of the current values. The controller is configured to selectively detect a first capacitor fault in response to concurrent determination that (i) the first power factor value is less than a first power factor threshold and (ii) a first current value of the current values is greater than a first current threshold. The first capacitor fault indicates that a capacitance of the capacitor has degraded.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/705,373, filed on Sep. 25, 2012. The entire disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to compressors and, more particularly, to systems and methods of control and diagnostics for a compressor with a run capacitor.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Compressors are used in a variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically “refrigeration systems”) to provide a desired heating or cooling effect. A compressor may include an electric motor to provide torque to drive the compressor to compress vapor refrigerant. The electric motor may be powered by an alternating current (AC) or direct current (DC) power supply. In the case of an AC power supply, single or poly-phase AC may be delivered to windings of the electric motor.

For a single-phase power supply, the refrigeration system may include a run capacitor used to initially store and supply power to the compressor. The run capacitor, however, may become faulty either with capacitance degradation or complete loss of capacitance (i.e., an open circuit condition). For example, capacitance degradation or complete loss of capacitance may occur after a period of use due to aging or overheating. A run capacitor with degraded capacitance may cause the compressor to perform below a desired capacity and/or efficiency performance standard. A run capacitor with zero capacitance may cause a start circuit for the compressor to be open, which could result in, for example, a locked rotor trip of a corresponding motor protector circuit shortly after motor start-up. In such case, the electric motor may not provide the compressor with enough torque to rotate, resulting in no cooling production and in an interruption in operation and use of the refrigeration system. Accordingly, a system designed to predict a run capacitor fault, such as capacitance degradation or complete loss of capacitance, is desired.

SUMMARY

A system is provided comprising a power supply that generates an alternating current power for powering a compressor with a capacitor, a voltage sensor that measures a plurality of voltage values based on the alternating current power, a current sensor that measures a plurality of current values based on the alternating current power, and a controller. The controller communicates with the voltage sensor and the current sensor and determines a power factor value based on at least one of the plurality of voltage values and at least one of the plurality of current values. The controller also determines a fault in the capacitor based on the power factor and at least one of the plurality of current values.

A method is provided comprising generating, with a power supply, an alternating current power for powering a compressor with a capacitor, measuring, with a voltage sensor, a plurality of voltage values based on the alternating current power, and measuring, with a current sensor, a plurality of current values based on the alternating current power. The method also comprises determining, with a controller in communication with the voltage sensor and the current sensor, a power factor value based on at least one of the plurality of voltage values and at least one of the plurality of current values, determining, with the controller, a fault in the capacitor based on the power factor and at least one of the plurality of current values; and communicating the fault in the capacitor from the controller to at least one of a user, a service person, a system controller, a remote server, a thermostat, a mobile device, and an email address.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic illustration of a refrigeration system.

FIG. 2 is a block diagram of a refrigeration system.

FIG. 2a is a schematic illustration of a compressor motor.

FIG. 3 is a block diagram of controller with a run capacitor fault determination system.

FIG. 4 is a graph showing a run capacitor fault event.

FIG. 5 is flow diagram for a control algorithm according to the present disclosure.

DETAILED DESCRIPTION

With reference to FIG. 1, an exemplary refrigeration system 10 may include a compressor 12. Compressor 12 may be a reciprocating compressor, a scroll type compressor, or another type of compressor. Compressor 12 may be equipped with an electric motor to compress refrigerant vapor that is delivered to a condenser 16 where the refrigerant vapor is liquefied at high pressure, thereby rejecting heat to the outside air. Condenser 16 may include a condenser fan 17, driven by an electric motor 18 that circulates air across coils of the condenser 16. The liquid refrigerant exiting the condenser 16 is delivered to an evaporator 20. As hot air moves across the evaporator, the liquid turns into gas, thereby removing heat from the air and cooling a refrigerated space. This low pressure gas is delivered to the compressor 12 and again compressed to a high pressure gas to start the refrigeration cycle again. While the refrigeration system 10 is shown with one compressor 12, a condenser 16, and an evaporator 20 in FIG. 1, the refrigeration system 10 may be configured with any number of compressors 12, condensers 18, evaporators 20, or other refrigeration system components.

Compressor 12 may be equipped with a controller 24. As described herein, controller 24 may monitor electric power delivered to compressor 12 and to the electric motor 18 that drives the condenser fan 17 with one or more voltage sensors and one or more current sensors. Based on electrical power measurements over time, such as electric current (I) and voltage (V), controller 24 may determine and monitor apparent power, actual power, power consumption, and power factor calculations for the electric motor of the compressor 12 over time.

Controller 24 may monitor and control operation of compressor 12 based on the electric current (I) and voltage (V) measurements and based on other compressor and refrigeration system data received from other compressor or refrigeration system sensors.

Controller 24 may activate or deactivate compressor 12 based on data received from the one or more voltage sensors and the one or more current sensors. For example, controller 24 may deactivate compressor 12 based on an excessive current or voltage condition, a deficient current or voltage condition, a current or voltage imbalance condition, or a loss of phase or current delay condition (if poly-phase electric power is used).

Controller 24 may be used and configured to control the overall operation of the refrigeration system 10. Controller 24 may monitor refrigeration system operating conditions, such as condenser temperatures and pressures, and evaporator temperatures and pressures, as well as environmental conditions, such as ambient temperature, to determine refrigeration system load and demand. For example, controller 24 may receive a compressor discharge temperature value from a compressor discharge temperature sensor 50. Alternatively, a compressor discharge pressure sensor may be used. Additionally, controller 24 may receive a condenser temperature value from a condenser temperature sensor 51 located at condenser 16. Alternatively, a condenser pressure sensor may be used. In addition, refrigeration system 10 may include multiple controllers working together to control refrigeration system. For example, controller 24 may be an outdoor unit controller located at an outdoor unit that includes the compressor 12, condenser 16, and condenser fan 17 with electric motor 18. In such case, controller 24 may communicate with, for example, an indoor unit controller and/or an indoor thermostat, which may monitor indoor conditions, such as an indoor temperature, and communicate activation or deactivation commands, or capacity demand instructions, to controller 24. Controller 24 may receive the commands or instructions and appropriately control the components of the outdoor unit, i.e., compressor 12 and condenser fan 17 with electric motor 18, based on the received commands or instructions. Controller 24 may adjust set-points based on operating conditions to maximize efficiency of refrigeration system 10 or may receive appropriate instructions from an indoor unit controller or indoor thermostat to adjust set-points to maximize efficiency. Controller 24 may also monitor a temperature of supply air and a temperature of return air of an indoor unit of the refrigeration system 10. Alternatively, an indoor unit controller or indoor thermostat may monitor the temperature of supply air and the temperature of return air of the indoor unit and may communicate such data to controller 24. Controller 24 may evaluate efficiency based on electric power measurements and calculations as described below.

With reference to FIG. 2, a block diagram of the refrigeration system 10 is shown in an HVAC application. For example, the refrigeration system 10 may be installed in an HVAC application wherein an indoor unit 104 includes evaporator 20 (FIG. 1) and an air handler unit and is located within a building, such as an office, retail store, or home, and wherein an outdoor unit includes compressor 12, condenser 16, and condenser fan 17 with electric motor 18. The refrigeration system 10 includes an alternating current (AC) power supply 120 that supplies electric power to an electric motor 148 of compressor 12 and to electric motor 18 for driving condenser fan 17. The indoor unit 104 supplies conditioned air (supply air) through a duct system. The air passes through the duct system and returns (return air) to the indoor unit 104. The indoor unit 104 includes a supply air temperature sensor 124 and a return air temperature sensor 128. The supply air temperature sensor 124 senses a supply air temperature supplied by the indoor unit 104 and communicates the supply air temperature to controller 24. Similarly, the return air temperature sensor 128 monitors a return air temperature returned to the indoor unit 104 and communicates the return air temperature to controller 24. As discussed above, the supply air temperature sensor 124 and the return air temperature sensor 128 may also communicate supply air temperature and return air temperature data to an indoor unit controller and/or indoor thermostat, which may, in turn, communicate the supply air temperature and return air temperature data to controller 24.

The power supply 120 is electrically coupled to the compressor 12 and condenser fan 17 via electrical terminals L1 and L2. In this way, the power supply 120 supplies power to the electric motor 148 of the compressor 12 and to the electric motor 18 of the condenser fan 17. The compressor 12 may also be electrically coupled to a run capacitor 132 and a contactor switch 136. The run capacitor 132 is arranged between the power supply 120 and the compressor 12. The run capacitor 132 stores power supplied by the power supply 120, when the refrigeration system 10 is powered on. When the refrigeration system 10 is powered on, the contactor switch 136 is electrically or mechanically closed by controller 24 to allow current to flow to the compressor 12. When the contactor switch 136 is closed, power is supplied to the condenser fan 17 and to the run capacitor 132. The run capacitor 132 stores power supplied by the power supply 120. The run capacitor 132 then provides initial power to the compressor 12 by supplying the stored power to the compressor 12.

Referring now to FIG. 2a , a schematic of the compressor motor 148 is shown. The compressor motor 148 includes a stator with a plurality of windings, including a start winding 152 and a run winding 156. The start winding 152 is connected between a start point (S) 150 and a common point (C) 149. The run winding 156 is connected between a run point (R) 151 and the common point (C) 149. The start point (S) 150 and the run point (R) 151 are each connected to electrical terminal L1. The common point (C) 149 is connected to electrical terminal L2. The compressor motor 148 may also include a rotor (not shown). Current through the windings causes the rotor to rotate and the compressor motor 148 to run. For example, when the refrigeration system 10 is powered on, current through the start winding 152 energizes the stator. The stator energy then causes the rotor to turn. The compressor motor 148 is powered by the turning rotor. The current through the run winding 156 maintains power to the stator through a power cycle. The run capacitor 132 is electrically coupled in series with the start winding 152, for example, between the start point (S) 150 and electrical terminal L1. In this way, the run capacitor 132 stores power supplied by the power supply 120 and provides an initial current to the stator through the start winding 152.

With reference again to FIG. 2, the refrigeration system 10 also includes a voltage sensor 140 and a current sensor 144. The voltage sensor 140 senses a voltage value of power being supplied to the compressor 12 and condenser fan 17 and communicates the voltage value to the controller 24. For example, the voltage sensor 140 may measure voltage on the incoming power line connected to electrical terminal L1 or across the run capacitor 132. The current sensor 144 senses a current value of line power being supplied to the compressor 12 and the electric motor 18 of the condenser fan 17 and communicates the current value to the controller 24. The current sensor 144 can also be located at the run capacitor 132 to sense current through the run capacitor 132 in series with the start winding 152 (FIG. 2).

The controller 24 receives sample current and voltage measurements periodically over each cycle of AC power to determine multiple instantaneous current and voltage measurements. For example, controller 24 may receive current and voltage measurements twenty times per cycle or approximately once every millisecond in the case of alternating current with a frequency of sixty hertz. From these actual current and voltage measurements, the controller 24 may calculate additional power related data such as true and apparent power, power consumption over time, and power factor.

Based on actual current and voltage measurements, the controller 24 may determine a root mean square (RMS) value for voltage and current. The controller 24 may calculate an RMS voltage value by squaring each of the sampled voltage measurements, averaging the squared measurements, and calculating the square root of the average. Likewise, the controller 24 may calculate an RMS current value by squaring each of the sampled current measurements, averaging the squared measurements, and calculating the square root of the average.

From RMS voltage and RMS current calculations, the controller 24 may calculate apparent power (S) according to the following equation: S=V _(RMS) ×I _(RMS),  (1) where V_(RMS) is the calculated RMS of voltage over at least one cycle of AC and where I_(RMS) is the calculated RMS of current over at least one cycle of AC. Apparent power may be calculated in units of Volt-Amps (VA) or kilo-Volt-Amps (kVA)

For three-phase power, the controller 24 may calculate apparent power for each phase of AC power. The controller 24 may calculate total apparent power (S_(Total)) for an electric motor of compressor 12 based on apparent power calculations for each of the phases, according to the following equation: S _(Total) =V _(RMS(1)) ×I _(RMS(1)) +V _(RMS(2)) ×I _(RMS(2)) +V _(RMS(3)) ×I _(RMS(3)),  (2) where V_(RMS(1)), V_(RMS(2)), and V_(RMS(3)) are the calculated RMS voltage over a cycle of AC for the first, second, and third phase of AC, respectively, and where I_(RMS(1)), I_(RMS(2)), and I_(RMS(3)) are the calculated RMS current over a cycle of AC for the first, second, and third phase of AC, respectively. Apparent power is calculated in units of Volt-Amps (VA) or kilo-Volt-Amps (kVA)

Active power (P), in units of watts (W) or kilo-watts (kW) may be calculated as an integral of the product of instantaneous currents and voltages over a cycle of AC, according to the following equation:

$\begin{matrix} {{P = {\frac{1}{T}{\int_{0}^{T}{\left( {{v(t)}{i(t)}} \right){\mathbb{d}t}}}}},} & (3) \end{matrix}$ where v(t) is instantaneous voltage at time t, in units of volts; where i(t) is instantaneous current at time t, in units of amps; and where T is the period of the line cycle frequency (for example, 16.3 milliseconds for 60 hertz power).

Based on the actual instantaneous electrical current and voltage measurements sampled over a cycle of the AC power, controller 24 may calculate (P) as the sum of the products of instantaneous voltage and current samples for each sample interval (e.g., one millisecond), over one cycle of AC. Thus, P may be calculated by controller 24 according to the following equation:

$\begin{matrix} {{P \cong {\frac{1}{T}{\sum\limits_{k = 1}^{k = \frac{T}{\Delta\; t}}{{v(k)}{i(k)}\Delta\; t}}}},} & (4) \end{matrix}$ where v(k) is the instantaneous voltage measurement for the kth sample; i(k) is the instantaneous current measurement for the kth sample; T is the period; and Δt is the sampling interval (e.g., 1 millisecond).

In a poly-phase system, P may be calculated for each phase of electric power. For example, in a three-phase system, the controller 24 may calculate a total active power (P_(Total) (P) by adding the active power for each phase, (P according to the following equation: P _(Total) =P ₍₁₎ +P ₍₂₎ +P ₍₃₎,  (5) where P₍₁₎, P₍₂₎, and P₍₃₎ are the active power for the first, second, and third phase of AC, respectively.

Based on the active power calculations, the controller 24 may calculate energy consumption by calculating an average of active power for each unit of time and integrating over a certain time period such as days, months or years. Energy consumption may be calculated by the controller 24 in units of watt-hours (WH) or kilo-watt-hours (kWH).

Further, based on the active power calculation and the apparent power calculation, the controller 24 may calculate the power factor (PF) according to the following equation:

$\begin{matrix} {{{PF} = \frac{P}{S}},} & (6) \end{matrix}$ where P is active power in units of watts (W) or kilo-watts (kW); and where S is apparent power in units of volt-amps (VA) or kilo-volt-amps (kVA). Generally, PF is the ratio of the power consumed to the power drawn. The controller 24 may calculate PF for each phase of electric power. The controller 24 may also calculate a total PF as a ratio of total actual power to total apparent power, according to the following equation:

$\begin{matrix} {{{PF}_{Total} = \frac{P_{Total}}{S_{Total}}},} & (7) \end{matrix}$

-   -   where P_(total) and S_(Total) are calculated according to         formulas 2 and 5 above.

Alternatively, the controller 24 may calculate power factor by comparing the zero crossings of the voltage and current waveforms. The processor may use the angular difference between the zero crossings as an estimate of PF. The controller 24 may monitor voltage and current measurements to determine voltage and current waveforms for AC power. Based on the measurements, the controller 24 may determine where each waveform crosses the zero axis. By comparing the two zero crossings, the controller 24 may determine an angular difference between the voltage waveform and the current waveform. The current waveform may lag the voltage waveform, and the angular difference may be used by the controller 24 as an estimate of PF.

PF may be used as an indication of the efficiency of the electric motor, or the compressor. Increased lag between the current waveform and the voltage waveform results in a lower power factor. A power factor near one, i.e., a unity power factor, is more desirable than a lower power factor. An electric motor with a lower power factor may require more energy to operate, thereby resulting in increased power consumption. Additionally, utility providers may impose a tariff for equipment operating below a pre-determined PF value.

PF may also be used as an indication of a fault in a system component, such as the run capacitor 132. For example, the controller 24 may determine a fault in the run capacitor 132 based on a PF value and a current value. Further, the controller 24 may confirm the impact or result of the capacitor fault by detecting a stable air-side circuit temperature, as described in further detail below, based on the air temperature difference or temperature split (TS) between the supply air and return air of the indoor unit 104. Alternatively or additionally, the controller 24 may confirm the impact or result of the capacitor fault by detecting a stable outdoor unit temperature, for example compressor discharge temperature, as sensed by the compressor discharge temperature sensor 50 (FIG. 1) or condenser temperature, as sensed by the condenser temperature sensor 51 (FIG. 1). A stable outdoor unit temperature condition may exist, for example, when the compressor discharge temperature and/or the condenser temperature remain relatively unchanged, or stable, despite operation of the refrigeration system 10.

With particular reference to FIG. 3, a block diagram of an example run capacitor fault determination system 200 is shown. The run capacitor fault determination system 200 includes the supply air temperature sensor 124, the return air temperature sensor 128, and controller 24. The controller 24 includes a temperature split (TS) determination module 216, a current/voltage monitor module 220, and a run capacitor status module 224. The TS determination module 216 determines a difference in temperature between supply air temperature and return air temperature. For example, as described in FIG. 2, the supply air temperature sensor 124 monitors a supply air temperature of air supplied by the indoor unit 104. The supply air temperature sensor 124 communicates the supply air temperature to the TS determination module 216. Similarly, the return air temperature sensor 128 monitors return air temperature of air returned to the indoor unit 104. The return air temperature sensor 128 communicates the return air temperature to the TS determination module 216. The TS determination module 216 determines an air temperature change value by subtracting the return air temperature value from the supply air temperature value. The TS determination module 216 communicates the air temperature difference value to the run capacitor status module 224. The functionality of the TS determination module 216 may also be performed by an indoor unit controller, which may receive the supply air temperature value and the return air temperature value from the supply air temperature sensor 124 and the return air temperature sensor 128 and may communicate the difference, or temperature split (TS) to controller 24 and/or to the run capacitor status module 224.

The current/voltage monitor module 220 receives current and voltage measurements from the voltage sensor 140 and the current sensor 144. The current/voltage monitor module 220 determines when measured current is above a predetermined current threshold. For example, the predetermined current threshold may be a current value indicative of a sudden increase in a total current demand. For example, an increase in current demand from the compressor 12 or the condenser fan 17 may contribute to an increase in the total current demand. The current/voltage monitor module 220 communicates current values above the predetermined current threshold to the run capacitor status module 224. The current/voltage monitor module 220 also calculates a power factor (as described above) based on the current and voltage measurements. The current/voltage monitor module 220 communicates the PF to the run capacitor status module 224. The run capacitor status module 224 and the current/voltage monitor module 220 can be separate modules or, alternatively, can be integrated into a single module. Further, the functionality and processing performed by the run capacitor status module 224 can alternatively be performed outside of controller 24. For example, the functionality and processing performed by the run capacitor status module 224 can be performed by an indoor unit controller, an indoor thermostat, or a refrigeration system controller. Additionally, the functionality and processing performed by the run capacitor status module 224 can be performed by a remote server, for example a cloud server that receives and monitors data for the refrigeration system 10. For example, the functionality and processing performed by the run capacitor status module 224 can be performed by remote server 228 shown in FIG. 3.

The run capacitor status module 224 determines a fault in a run capacitor, for example the run capacitor 132, based on the calculated PF, the current measurements, and the confirming air temperature difference value. For example, the run capacitor status module 224 determines whether a sudden drop in PF has occurred. The run capacitor status module 224 receives a first PF value and a second PF value from the current/voltage monitor module 220. The run capacitor status module 224 compares the second PF value to the first PF value. The run capacitor status module 224 determines a sudden drop in PF when a difference between the first PF value and the second PF value is greater than a predetermined threshold and when the drop in PF has occurred within a predetermined period of time. For example only, the run capacitor status module 224 may determine that a drop in PF is a sudden drop in PF when the first PF value is 10% greater than the second PF value during a time period of 15 seconds. It is understood, however, that other percentage drops and other time periods can be used.

The run capacitor status module 224 then determines whether the difference between the supply air temperature value and the return air temperature value is indicative of a stable condition, i.e., whether TS is stable and has not dropped towards zero. The run capacitor status module 224 receives the air temperature difference value from the TS determination module 216. The run capacitor status module 224 determines that TS is stable when the air temperature difference value is less than a predetermined temperature difference threshold. Conversely, the run capacitor status module 224 determines that TS is not stable when the air temperature difference value is below a predetermined temperature difference threshold near zero. As discussed above, alternatively or additionally, the run capacitor status module may confirm the impact or result of the capacitor fault by detecting a stable outdoor unit temperature, for example compressor discharge temperature, as sensed by the compressor discharge temperature sensor 50 (FIG. 1) or condenser temperature, as sensed by the condenser temperature sensor 51 (FIG. 1).

The run capacitor status module 224 also monitors the current values received from the current/voltage monitor module 220. The run capacitor status module 224 determines a fault in the run capacitor 132, such as a drop in capacitance, when there has been a sudden drop in PF, coupled with a stable TS condition, and a current value above a predetermined current threshold. As discussed above, a stable outdoor unit temperature condition can be used in addition to, or instead of, the stable TS condition. When these conditions occur, the run capacitor status module 224 may determine that a run capacitor fault has occurred or will occur in the near future and may deactivate the compressor 12 to avoid damage to the compressor 12 or other system components.

In another embodiment, the run capacitor status module 224 can determine a fault in the run capacitor 132 when there has been a sudden drop in PF coupled with a current value above a predetermined current threshold. When these conditions occur, the run capacitor status module 224 may determine that a run capacitor fault has occurred or will occur in the near future and may deactivate the compressor 12 to avoid damage to the compressor 12 or other system components.

In another embodiment, the run capacitor status module 224 can determine an open run capacitor fault when there is no current flowing through the run capacitor 132 and the start winding 152, and when the TS is at or near zero. When these conditions occur, the run capacitor status module 224 may determine that an open run capacitor fault has occurred and that the compressor may subsequently experience a locked-rotor motor trip. In such case, controller 24 may deactivate the compressor 12 to avoid damage to the compressor 12 or other system components. Alternatively, the run capacitor status module 224 may determine an open run capacitor fault when there is no current flowing through the run capacitor 132 and the start winding 152, and when there is no change or increase in an outdoor unit temperature, such as the compressor discharge temperature, as sensed by the compressor discharge temperature sensor 50 (FIG. 1), or the condenser temperature, as sensed by the condenser temperature sensor 51 (FIG. 1). For example, during normal operation the compressor discharge temperature and the condenser temperature increase after startup of the compressor. If, on the other hand, there is no increase in the compressor discharge temperature and/or the condenser temperature, in combination with no current flowing through the run capacitor 132 and the start winding 152, the run capacitor status module 224 may determine that an open run capacitor fault has occurred. Additionally or alternatively, the compressor discharge temperature and/or the condenser temperature may be compared with ambient temperature to determine whether the compressor discharge temperature and/or the condenser temperature are converging towards the ambient temperature. If such a condition exists in combination with no current flowing through the run capacitor 132 and the start winding 152, the run capacitor status module 224 may determine that an open run capacitor fault has occurred.

In another embodiment, the run capacitor status module 224 may determine that the run capacitor 132 has been incorrectly installed, for example when the wrong type of capacitor has been installed after initial installation or after a replacement service, when PF is below a pre-determined value, such as, for example, 90%. Typically, the compressor manufacturer optimizes the run capacitor selection such that the PF is at least 90%. When these conditions occur, the run capacitor status module 224 may determine that a run capacitor fault has occurred and that the compressor may subsequently experience a locked-rotor motor trip. In such case, controller 24 may deactivate the compressor 12 to avoid damage to the compressor 12 or other system components.

The run capacitor status module 224 may also communicate an alert to a remote server 228. For example, when the run capacitor status module 224 determines that a run capacitor fault has occurred, the run capacitor status module 224 may communicate an alert indicative of the run capacitor fault to the remote server 228. The remote server 228 may be a cloud service, a cluster of servers, or an internet application. The remote server 228 may then communicate the alert to an alert recipient 229, such as a home owner, a service person, or both. Alternatively or additionally, the remote server 228 may also communicate the alert to other alert recipients 229, such as a thermostat coupled to refrigeration system 10, a mobile device, or an e-mail address. In another example, the run capacitor status module 224 may communicate the alert directly to the alert recipient 229, such as the thermostat, the mobile device, or the e-mail address. The run capacitor status module 224 may also display the alert locally, such as on a display of the controller 24. For example, an LED display of the controller 24 may communicate an alert to a contractor using a diagnostic code.

With reference to FIG. 4, a graphical depiction of a run capacitor fault event 300 is shown. The run capacitor fault event 300 is a graphical depiction of current, TS, and PF over an event period of time. The vertical axis of the run capacitor fault event 300 includes various different scales. Each of the current, TS, and PF values are represented on a single scale in order to illustrate a relative relationship between current, TS, and PF. The run capacitor fault event 300 includes a TS graph 304, a current graph 308, and a PF graph 312. The run capacitor fault event 300 also includes a capacitor fault line 316 (indicating an open capacitor condition) and a fault prediction line 320 (indicating a degraded capacitance condition). The TS line 304 depicts a plurality of TS values over the event period. For example, starting at the left of the graph and proceeding forward in time to the right of the graph, the TS graph 304 begins at a first TS value and remains stable until the capacitor fault line 316. The TS graph 304 then decreases to a value indicative of a run capacitor fault.

The current graph 308 depicts current measurements over the event period. For example, the current graph 308 begins at a first value. The current graph 308 increases at the fault prediction line 320. The PF graph 312 depicts calculated PF values over the event period. The PF graph 312 begins at a first PF value. The PF line 312 decreases to a second PF value at the fault prediction line 320.

At the fault prediction line 320, the PF graph 312 is indicative of a sudden drop in PF indicative of a sudden significant drop in capacitance, the current graph 308 is indicative of a sudden increase in current draw, and the TS graph 304 is indicative of a relatively stable TS condition. At the fault prediction line 320, the conditions are present to predict or forecast a future or impending fault in the run capacitor. At the capacitor fault line 316, the sudden change in TS to almost zero, as shown by the TS line 304, indicates a fault in the run capacitor (i.e., a zero capacitance/open capacitor condition). The open run capacitor 132, for example, can create an open start winding 152 condition and will not cause the compressor 12 to cause a locked-rotor trip of a motor protector circuit at start up. In such case, the electric motor 148 will not be able to rotate the compressor 12.

With reference to FIG. 5, an example method for run capacitor fault prediction 400 starts at 404. At 404, the method 400 receives current measurements and voltage measurements. At 412, the method 400 calculates a PF value based on the current measurements and the voltage measurements. At 416, the method 400 determines whether a sudden drop in PF has occurred. If false, the method 400 continues at 408. If true, the method 400 continues at 420. At 420, the method determines whether an increase in current draw has occurred based on the current measurement. If false, the method 400 continues at 416. If true, the method 400 continues at 424. At 424, the method 400 receives a supply air temperature and a return air temperature. At 428, the method 400 calculates a TS value based on the difference between the supply air temperature and the return air temperature. At 432, the method 400 determines whether TS is stable based on the TS value. If false, the method 400 continues at 408. If true, the method 400 continues at 436. At 436, the method 400 deactivates a compressor and/or sends an alert indicative of a fault in the run capacitor to a remote server or to an alert recipient. The method 400 ends at 440.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

As used herein, the term controller or module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term controller or module may include memory (shared, dedicated, or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors. In addition, some or all code from a single module may be stored using a group of memories.

The apparatuses and methods described herein may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data. Non-limiting examples of the non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage. 

What is claimed is:
 1. An apparatus comprising: a voltage sensor that measures a plurality of voltage values of alternating current power supplied to a capacitor, wherein the capacitor is electrically coupled to a compressor; a current sensor that measures a plurality of current values of the alternating current power; and a controller configured to: receive the plurality of voltage values; receive the plurality of current values; determine a first power factor value based on at least one of the plurality of voltage values and at least one of the plurality of current values; and selectively detect a first capacitor fault in response to concurrent determination that (i) the first power factor value is less than a first power factor threshold and (ii) a first current value of the plurality of current values is greater than a first current threshold, wherein the first capacitor fault indicates that a capacitance of the capacitor has degraded.
 2. A system comprising; the apparatus of claim 1; the compressor; and the capacitor.
 3. The apparatus of claim 1 wherein the controller is configured to disable the compressor in response to detection of the first capacitor fault.
 4. The apparatus of claim 1 wherein the controller is configured to detect the first capacitor fault in response to concurrent determination that (i) a measured temperature value is stable, (ii) the first power factor value is less than the first power factor threshold, and (iii) the first current value is greater than the first current threshold.
 5. The apparatus of claim 4 wherein the measured temperature value comprises a difference between a supply air temperature and a return air temperature, wherein the supply air temperature and the return air temperature are measured on opposite sides of an evaporator associated with the compressor.
 6. The apparatus of claim 4 wherein the measured temperature value comprises one of (i) a refrigerant temperature at a discharge side of the compressor or (ii) a refrigerant temperature at a condensing coil associated with the compressor.
 7. The apparatus of claim 4 wherein the controller is configured to determine the first power factor threshold by subtracting a predetermined offset from a previous power factor value.
 8. The apparatus of claim 7 wherein the controller is configured to determine the first power factor threshold as 10% less than a power factor value determined 15 seconds earlier.
 9. The apparatus of claim 4 wherein the controller is configured to determine the first current threshold by adding a predetermined offset to a previous one of the plurality of current values.
 10. The apparatus of claim 1 wherein the controller is configured to detect a second capacitor fault in response to the power factor value being below a predetermined threshold subsequent to installation of the capacitor, wherein the second capacitor fault indicates that the capacitor is an incorrect type.
 11. The apparatus of claim 1 wherein the controller is configured to detect a second capacitor fault in response to concurrent determination that (i) zero current is flowing through the capacitor and (ii) a measured temperature value is below a predetermined threshold, wherein the second capacitor fault indicates that the capacitor is an open circuit.
 12. The apparatus of claim 11 wherein the measured temperature value comprises one of (i) a difference between a supply air temperature and a return air temperature, (ii) a refrigerant temperature at a discharge side of the compressor, or (iii) a refrigerant temperature at a condensing coil associated with the compressor, wherein the supply air temperature and the return air temperature are measured on opposite sides of an evaporator associated with the compressor.
 13. A method comprising: measuring a plurality of voltage values of alternating current power supplied to a capacitor, wherein the capacitor is electrically coupled to a compressor; measuring a plurality of current values of the alternating current power; determining a first power factor value based on at least one of the plurality of voltage values and at least one of the plurality of current values; and selectively detecting a first capacitor fault in response to concurrent determination that (i) the first power factor value is less than a first power factor threshold and (ii) a first current value of the plurality of current values is greater than a first current threshold, wherein the first capacitor fault indicates that a capacitance of the capacitor has degraded.
 14. The method of claim 13 further comprising disabling the compressor in response to detection of the first capacitor fault.
 15. The method of claim 13 further comprising detecting the first capacitor fault in response to concurrent determination that (i) a measured temperature value is stable, (ii) the first power factor value is less than the first power factor threshold, and (iii) the first current value is greater than the first current threshold.
 16. The method of claim 15 wherein the measured temperature value comprises a difference between a supply air temperature and a return air temperature, wherein the supply air temperature and the return air temperature are measured on opposite sides of an evaporator associated with the compressor.
 17. The method of claim 15 wherein the measured temperature value comprises one of (i) a refrigerant temperature at a discharge side of the compressor or (ii) a refrigerant temperature at a condensing coil associated with the compressor.
 18. The method of claim 15 further comprising determining the first power factor threshold by subtracting a predetermined offset from a previous power factor value.
 19. The method of claim 18 further comprising determining the first power factor threshold as 10% less than a power factor value determined 15 seconds earlier.
 20. The method of claim 15 further comprising determining the first current threshold by adding a predetermined offset to a previous one of the plurality of current values.
 21. The method of claim 13 further comprising detecting a second capacitor fault in response to the power factor value being below a predetermined threshold subsequent to installation of the capacitor, wherein the second capacitor fault indicates that the capacitor is an incorrect type.
 22. The method of claim 13 further comprising detecting a second capacitor fault in response to concurrent determination that (i) zero current is flowing through the capacitor and (ii) a measured temperature value is below a predetermined threshold, wherein the second capacitor fault indicates that the capacitor is an open circuit.
 23. The method of claim 22 wherein the measured temperature value comprises one of (i) a difference between a supply air temperature and a return air temperature, (ii) a refrigerant temperature at a discharge side of the compressor, or (iii) a refrigerant temperature at a condensing coil associated with the compressor, wherein the supply air temperature and the return air temperature are measured on opposite sides of an evaporator associated with the compressor.
 24. A non-transitory computer-readable medium storing instructions executable on a processor, the instructions comprising: measuring a plurality of voltage values of alternating current power supplied to a capacitor, wherein the capacitor is electrically coupled to a compressor; measuring a plurality of current values of the alternating current power; determining a first power factor value based on at least one of the plurality of voltage values and at least one of the plurality of current values; and selectively detecting a first capacitor fault in response to concurrent determination that (i) the first power factor value is less than a first power factor threshold and (ii) a first current value of the plurality of current values is greater than a first current threshold, wherein the first capacitor fault indicates that a capacitance of the capacitor has degraded. 